The proposed work represents the continuation of a comprehensive study of the structure and function of the renal lymphatic system. The morphological aspect of the work involves a qualitative and quantitative assessment of the intra-renal lymphatic vessels and their relationships with other elements of the renal parenchyma. Special attention will be paid to lymphatic drainage of the renal medulla. Included is a study on the mechanisms of transport across lymphatic endothelial walls, involving the use of tracer substances, under control and experimental conditions. It is expected that these various experiments will provide a detailed picture of the pattern and distribution of renal lymphatics, an analysis of the mechanism whereby interstitial fluid becomes lymph in its transport across the endothelial wall, and an estimate of the quantity of lymph within the kidney. Functional studies are in progress whereby the renin content of renal lymph is used as an indication of intrarenal interstitial concentrations under differing conditions of renal function. These renin concentrations will be correlated with measurements of renin secretion obtained from renal arterio venous concentration differences. These experiments will provide information on the mechanisms of the intrarenal role of renin in kidney function.